Update git submodules

* Update docs/submodules/yardstick from branch 'stable/danube'
  - Merge "Terminate openstack service process using kill command in HA test cases" into stable/danube
  - Terminate openstack service process using kill command in HA test cases

    JIRA: YARDSTICK-659

    In some openstack environment, the service process cannot be killed by killall
    command but can be terminate by kill command.
    This patch is about to switch to use kill command in the
    fault_process_kill.bash to kill processes.

    Change-Id: Iec455ee56d3f31fb5c16de5994870d1acd33f41a
    Signed-off-by: JingLu5 <lvjing5@huawei.com>
    (cherry picked from commit dd42ba3cafb908246da5b90c8bbbc2c7d0beb801)

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index a19d16b..9f576f2 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit a19d16bca4499604894c464cd9e2435bf85edefd
+Subproject commit 9f576f22b8233f4baea14e42786c1a07f8afecd9